1. Field of the Invention
The present invention relates to systems for automated counting of visible bacterial colonies in culture media (agar plates). In addition, the invention relates to automated colony counting systems for accurate counting of colonies under adverse colony crowding conditions and which have ability to discriminate between different parts of the culture medium to permit selection of those regions which will produce the best available measurement of the bacterial concentration of the sample contained in or on the culture medium.
2. Description of the Prior Art
Automated bacterial colony counting systems are commercially available for determinng the number of visible bacterial colonies in or on a culture medium such as a Petri dish. In the preferred embodiment of the present invention, a prior art commercially available bacteria colony counting system, the Model 500A Laser Bacteria Colony Counter, sold by Spiral System Instruments, Inc. of 4853 Cordell Avenue, Bethesda, Md. 20014, is used for providing raw counting data in the form of signals used for analysis of colonies with the present invention.
Various methods and apparatus for manually and automatically plating culture mediums with bacteria containing solutions are well known. U.S. Pat. Nos. 3,799,844, 3,892,632 and 3,962,040 disclose apparatus for plating bacteria containing solutions in a spiral. A commercially available instrument, known as the SPIRAL PLATER, which is manufactured under the aforementioned patents, can be programmed to deposit any desired volume of sample per unit length of the deposition path. The volume in any segment of a plate is determinable from knowledge of the control program deposition rate as a function of radial displacement of the dispensing stylus on the plate. Manual methods for applying bacteria containing solutions are exemplified by "pour" and "spread" plates. The visible colonies of the culture mediums produced by the aforementioned methods and apparatus are counted by either manual methods or an automated counting system as described in the above-referenced patents and commercially available Model 500A Laser Counter. Automated colony counting systems do not accurately distinguish overlapping colonies and, moreover, do not perform any analysis of the raw colony counts to eliminate the data of unreliable counts to increase reliablility of the assessment of bacterial concentration in the applied sample.